Tacrolimus (FK506) prevents early retinal neovascularization in streptozotocin-induced diabetic mice

Knockdown of thioredoxin interacting protein in Müller cells attenuates photoreceptor apoptosis in streptozotocin-induced diabetic mouse model

We explored the effect of inhibition of thioredoxin interacting protein (Txnip) on neuroprotection in Müller cells under high glucose. Wild-type (WT) and Txnip knockout (Txnip-/-) mice were used to establish a streptozotocin (STZ)-induced diabetes model and a Müller cells high glucose model. We detected BDNF expression and PI3K/AKT/CREB pathway activation levels in the retina and Müller cells of each group in vivo and in vitro experiments. The Txnip-/- STZ group showed higher expression of BDNF and phosphorylation of PI3K/AKT/CREB in retina, and less retinal photoreceptor apoptosis was observed in Txnip-/- diabetic group than in WT. After using an inhibitor of PI3K signaling pathway, BDNF expression was reduced; In vitro co-cultured with Müller cells in different groups, 661 W cells showed different situations, Txnip-/- Müller cells maximum downregulated Cleaved-caspase 3 expression in 661 W, accompanied by an increase in Bcl-2/Bax ratio. These findings indicate that inhibiting endogenous Txnip in mouse Müller cells can promote their expression and secretion of BDNF, thereby reducing HG induced photoreceptor apoptosis and having important neuroprotective effects on DR. The regulation of BDNF expression by Txnip may be achieved by activating the PI3K/AKT/CREB pathway. This study suggests that regulating Txnip may be a potential target for DR treatment.

The Role of Natural Products in Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most severe complications of diabetes mellitus and potentially leads to significant visual impairment and blindness. The complex mechanisms involved in the pathological changes in DR make it challenging to achieve satisfactory outcomes with existing treatments. Diets conducive to glycemic control have been shown to improve outcomes in diabetic patients, thus positioning dietary interventions as promising avenues for DR treatment. Investigations have demonstrated that natural products (NPs) may effectively manage DR. Many types of natural compounds, including saponins, phenols, terpenoids, flavonoids, saccharides, alkaloids, and vitamins, have been shown to exert anti-inflammatory, antioxidant, anti-neovascular, and antiapoptotic effects in vivo and in vitro. Nevertheless, the clinical application of NPs still faces challenges, such as suboptimal specificity, poor bioavailability, and a risk of toxicity. Prospective clinical studies are imperative to validate the therapeutic potential of NPs in delaying or preventing DR.

Manifestation of Pathology in Animal Models of Diabetic Retinopathy Is Delayed from the Onset of Diabetes

Diabetic retinopathy (DR) is the most common complication that develops in patients with diabetes mellitus (DM) and is the leading cause of blindness worldwide. Fortunately, sight-threatening forms of DR develop only after several decades of DM. This well-documented resilience to DR suggests that the retina is capable of protecting itself from DM-related damage and also that accumulation of such damage occurs only after deterioration of this resilience. Despite the enormous translational significance of this phenomenon, very little is known regarding the nature of resilience to DR. Rodent models of DR have been used extensively to study the nature of the DM-induced damage, i.e., cardinal features of DR. Many of these same animal models can be used to investigate resilience because DR is delayed from the onset of DM by several weeks or months. The purpose of this review is to provide a comprehensive overview of the literature describing the use of rodent models of DR in type-1 and type-2 diabetic animals, which most clearly document the delay between the onset of DM and the appearance of DR. These readily available experimental settings can be used to advance our current understanding of resilience to DR and thereby identify biomarkers and targets for novel, prevention-based approaches to manage patients at risk for developing DR.

Diabetic retinopathy: a comprehensive update on in vivo, in vitro and ex vivo experimental models

Diabetic retinopathy (DR), one of the leading causes of visual impairment and blindness worldwide, is one of the major microvascular complications in diabetes mellitus (DM). Globally, DR prevalence among DM patients is 25%, and 6% have vision-threatening problems among them. With the higher incidence of DM globally, more DR cases are expected to be seen in the future. In order to comprehend the pathophysiological mechanism of DR in humans and discover potential novel substances for the treatment of DR, investigations are typically conducted using various experimental models. Among the experimental models, in vivo models have contributed significantly to understanding DR pathogenesis. There are several types of in vivo models for DR research, which include chemical-induced, surgical-induced, diet-induced, and genetic models. Similarly, for the in vitro models, there are several cell types that are utilised in DR research, such as retinal endothelial cells, Müller cells, and glial cells. With the advancement of DR research, it is essential to have a comprehensive update on the various experimental models utilised to mimic DR environment. This review provides the update on the in vitro, in vivo, and ex vivo models used in DR research, focusing on their features, advantages, and limitations.

Tacrolimus Improves Therapeutic Efficacy of Umbilical Cord Blood-Derived Mesenchymal Stem Cells in Diabetic Retinopathy by Suppressing DRP1-Mediated Mitochondrial Fission

Diabetic retinopathy (DR) is a leading cause of blindness in diabetic patients. Umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) are emerging as a promising new drug for degenerative disease associated with diabetes. Recent studies have shown that high glucose-increased excessive calcium levels are a major risk factor for mitochondrial reactive oxygen species (mtROS) accumulation and apoptosis. This study aimed to investigate the role of high glucose-induced NFATC1 signaling in mitochondrial oxidative stress-stimulated apoptosis and the effect of tacrolimus on the therapeutic efficacy of subconjunctival transplantation of UCB-MSCs in a DR rat model. High glucose increased mtROS and cleaved caspase-9 expression in UCB-MSCs. High glucose conditions increased O-GlcNAcylated protein expression and nuclear translocation of NFATC1. Tacrolimus pretreatment recovered high glucose-induced mtROS levels and apoptosis. In the DR rat model, subconjunctival transplantation of tacrolimus-pretreated MSCs improved retinal vessel formation, retinal function, and uveitis. In high glucose conditions, tacrolimus pretreatment reduced protein and mRNA expression levels of DRP1 and inhibited mitochondrial fission. In conclusion, we demonstrated that high glucose-induced O-GlcNAcylation activates NFATC1 signaling, which is important for DRP1-mediated mitochondrial fission and mitochondrial apoptosis. Finally, we proposed NFATC1 suppression by tacrolimus as a promising therapeutic strategy to improve the therapeutic efficacy of UCB-MSC transplantation for DR treatment.

Interleukin-17A attenuates photoreceptor cell apoptosis in streptozotocin-induced diabetic mouse model

Diabetic retinopathy (DR) represents an important microvascular complication of diabetes, which is the top etiology of vision impairment worldwide. Although interleukin (IL)-17A is increasingly implicated in DR development, the underlying cellular mechanisms remain poorly defined. This work aims to evaluate IL-17A levels in the retina of streptozotocin (STZ)-induced diabetic mice and elucidate their potential roles. We found IL-17A was upregulated in diabetic retina after intraperitoneal injection of STZ and high-glucose (HG)-cultured primary Müller cells. IL-17A knockout (IL-17A^−/−) downregulated glial fibrillary acidic protein (GFAP) and inhibited the conversion of proneurotrophin-3 (proNT-3) to mature NT-3 in retinal specimens from diabetic mice as well as in Müller cells cultured under HG conditions. Induced apoptosis and upregulated Bax and cleaved caspase-3 were observed in retinal specimens from IL-17A^−/− diabetic mice and photoreceptor (661 W) cells after co-culture with IL-17A^−/− Müller cells. Moreover, RNA interference-induced gene silencing of tyrosine kinase C receptor (TrkC) in 661 W cells reversed the anti-apoptotic effect of IL-17A under HG conditions. Taken together, our findings suggest that IL-17A/NT-3/TrkC axis regulation suppresses apoptosis in photoreceptor cells, providing a new treatment strategy for DR.

Animal models of diabetic retinopathy

The retina is the posterior neuro-integrated layer of the eye that conducts impulses induced by light to the optic nerve for human vision. Diseases of the retina often leads to diminished vision and in some cases blindness. Diabetes mellitus (DM) is a worldwide public health issue and globally, there is an estimated 463 million people that are affected by DM and its consequences. Diabetic retinopathy (DR) is a blinding complication of chronic uncontrolled DM and is the most common cause of blindness in the United States between the ages 24-75. It is estimated that the global prevalence of DR will increase to 191.0 million by 2030, of those 56.3 million possessing vision-threatening diabetic retinopathy (VTDR). For the most part, current treatment modalities control the complications of DR without addressing the underlying pathophysiology of the disease. Therefore, there is an unmet need for new therapeutics that not only repair the damaged retinal tissue, but also reverse the course of DR. The key element in developing these treatments is expanding our basic knowledge by studying DR pathogenesis in animal models of proliferative and non-proliferative DR (PDR and NPDR). There are numerous models available for the research of both PDR and NPDR with substantial overlap. Animal models available include those with genetic backgrounds prone to hyperglycemic states, immunologic etiologies, or environmentally induced disease. In this review we aimed to comprehensively summarize the available animal models for DR while also providing insight to each model's ocular therapeutic potential for drug discovery.

Effects of islet transplantation on microvascular and macrovascular complications in type 1 diabetes

Type 1 diabetes is associated with high morbidity and mortality from microvascular and macrovascular disease with considerable economic cost to society. Islet cell transplantation (ICT) is a treatment option recommended by National Institute for Health and Care Excellence (NICE) for people with debilitating hypoglycaemia due to type 1 diabetes, including those with renal failure where kidney transplantation may also be indicated. The primary aim of ICT is to improve glycaemic control, reduce severe hypoglycaemia, stabilise glycaemic variability and restore awareness of hypoglycaemia where this is compromised. Insulin independence, although not a primary aim, should also be considered a therapeutic goal. The impact ICT has on the progression of microvascular and macrovascular diabetes complications is derived from small studies and has not been examined in large clinical trials. Lifelong immunosuppression, which is necessary to avoid transplant rejection, has adverse effects on lipid metabolism, hypertension and renal function, which must also be considered. In this review, we discuss the role of ICT in type 1 diabetes management and the available evidence with respect to microvascular and macrovascular disease progression post-transplantation. We conclude that, following ICT, microvascular complications including retinopathy and neuropathy are stabilised or improved. Effects on nephropathy can be complicated by coexisting kidney transplantation and the impact of immunosuppression, the latter leading to an early decline in renal function; however, there is evidence to suggest stable renal outcomes in the long term. Short-term studies have demonstrated a positive impact of ICT on surrogate markers of macrovascular disease; however, long-term studies and trials in this area are lacking.

Self-Assembling Tacrolimus Nanomicelles for Retinal Drug Delivery

Neovascular age-related macular degeneration (AMD) is characterized by an increase in reactive oxygen species (ROS) and pro-inflammatory cytokines in the retinal pigment epithelium cells. The primary purpose of this study was the development of a clear, tacrolimus nanomicellar formulation (TAC-NMF) for AMD. The optimized formulation had a mean diameter of 15.41 nm, a zeta potential of 0.5 mV, and an entrapment efficiency of 97.13%. In-vitro cytotoxicity studies revealed the dose-dependent cytotoxicity of TAC-NMF on various ocular cell lines, such as human retinal pigment epithelium (D407), monkey retinal choroidal endothelial (RF/6A) cells, and human corneal epithelium (CCL 20.2) cells. Cellular uptake and in-vitro distribution studies using flow cytometry and confocal microscopy, respectively, indicated an elevated uptake of TAC-NMF in a time-dependent manner. Biocompatibility assay using macrophage RAW 264.7 cell line resulted in low production of inflammatory cytokines such as IL-6, IL-1β and TNF-α after treatment with TAC-NMF. There was a decrease in ROS in D407 cells pre-treated with sodium iodate (ROS inducing agent) after treating with TAC-NMF and tacrolimus drug. Similarly, there was a reduction in the pro-inflammatory cytokines and VEGF-A in D407 cells pretreated with sodium iodate. This indicates that TAC-NMF could lower pro-inflammatory cytokines and ROS commonly seen in AMD.

FK506 prevented bone loss in streptozotocin-induced diabetic rats via enhancing osteogenesis and inhibiting adipogenesis

Background

Type 1 diabetes mellitus (DM) is associated with severe osteoporosis, which is still a great challenge in the clinic. This work aimed to investigate the skeletal effects of FK506 in a rat model of streptozocin induced type 1 DM.

Methods

Rats were divided into three groups: control (CTL), DM rats and DM rats treated with FK506. Dual energy X-ray absorption, micro-computed tomography, bone mechanics and bone histology were used for skeletal analysis. Bone marrow adipocytes infiltrations were detected by oil red O stain and H&E stain. In addition, the protein expression of adipocyte-specific makers (PPAR-γ, C/EBP-αβ), osteoblast-specific markers (Runx2, Osterix) and nuclear translocation of β-catenin in femurs were determined by western blot.

Results

In the study, bone mineral density of femurs and lumbar vertebras in diabetic rats were increased after FK506 administration. FK506 treatment resulted in higher cancellous bone volume but had no significant effect on cortical bones in diabetic rats. The ultimate force and work to failure were increased in DM+FK506 group, while they were reduced in the DM group. Compared with the CTL, the infiltration of bone marrow adipocytes was significantly increased in the DM group, which was reduced after the treatment of FK506. Besides, the expression levels of Runx2 and Osterix were up-regulated, and that of PPAR-γ and C/EBP-α were down-regulated in diabetic rats after FK506 treatment. In addition, the nuclear translocation of β-catenin protein levels were increased in diabetic rats after the treatment of FK506.

Conclusions

Our study indicated that FK506 could alleviate bone loss in diabetic rats. This effects could be due to the results of enhancing osteogenesis and inhibiting adipogenesis, which might be regulated by activation the nuclear translocation of β-catenin.

Combinatory FK506 and Minocycline Treatment Alleviates Prion-Induced Neurodegenerative Events via Caspase-Mediated MAPK-NRF2 Pathway

Transcription factors play a significant role during the symptomatic onset and progression of prion diseases. We previously showed the immunomodulatory and nuclear factor of activated T cells’ (NFAT) suppressive effects of an immunosuppressant, FK506, in the symptomatic stage and an antibiotic, minocycline, in the pre-symptomatic stage of prion infection in hamsters. Here we used for the first time, a combinatory FK506+minocycline treatment to test its transcriptional modulating effects in the symptomatic stage of prion infection. Our results indicate that prolonged treatment with FK506+minocycline was effective in alleviating astrogliosis and neuronal death triggered by misfolded prions. Specifically, the combinatory therapy with FK506+minocycline lowered the expression of the astrocytes activation marker GFAP and of the microglial activation marker IBA-1, subsequently reducing the level of pro-inflammatory cytokines interleukin 1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α), and increasing the levels of anti-inflammatory cytokines IL-10 and IL-27. We further found that FK506+minocycline treatment inhibited mitogen-activated protein kinase (MAPK) p38 phosphorylation, NF-kB nuclear translocation, caspase expression, and enhanced phosphorylated cAMP response element-binding protein (pCREB) and phosphorylated Bcl2-associated death promoter (pBAD) levels to reduce cognitive impairment and apoptosis. Interestingly, FK506+minocycline reduced mitochondrial fragmentation and promoted nuclear factor–erythroid2-related factor-2 (NRF2)-heme oxygenase 1 (HO-1) pathway to enhance survival. Taken together, our results show that a therapeutic cocktail of FK506+minocycline is an attractive candidate for prolonged use in prion diseases and we encourage its further clinical development as a possible treatment for this disease.

Methylglyoxal-Induced Retinal Angiogenesis in Zebrafish Embryo: A Potential Animal Model of Neovascular Retinopathy

Methylglyoxal (MG) is an intermediate of glucose metabolism and the precursor of advanced glycation end products (AGEs) found in high levels in blood or tissue of diabetic patients. MG and AGEs are thought to play a major role in the pathogenesis of diabetic retinopathy. In order to determine if zebrafish is valuable to help us understand more about retinopathy, we evaluate if MG induces abnormal vascular change and angiogenesis in zebrafish in a short incubation period. We also used an inhibitor of VEGFR (PTK787) to explore the mechanistic role of VEGF in MG-induced pathogenesis. A transgenic Tg(flk1:GFP) zebrafish line was used, and the embryos were incubated with MG solution and in combination with glucose (to mimic hyperglycemia). Retinal vascular structure visible with fluorescence signal was imaged using fluorescence microscopy. The percentage of vascular area was calculated and found elevated in the MG treatment groups than that in the control group (p < 0.01) which indicated increased angiogenesis induced by MG treatment. PTK787 blocked the proangiogenic effects of MG treatment. This study suggests that MG has a potential proangiogenic effect via VEGF signaling in the retina of zebrafish embryos. Therefore, this zebrafish model may be used to study neovascular retinopathy.

A non-invasive nanoparticle mediated delivery of triamcinolone acetonide ameliorates diabetic retinopathy in rats

Diabetic retinopathy (DR) is a multifactorial manifestation associated with microvascular complications and is the fourth leading cause of visual impairment and blindness world-wide. Current day treatment of DR relies heavily on invasive techniques such as intravitreal injections of therapeutic agents. Unfortunately, intravitreal injections are associated with various complications such as intraocular bleeding, endophthalmitis, pain and discomfort resulting in poor patient compliance. To date, there has been no non-invasive drug delivery system reported for DR treatment. To address this, we developed a core-shell nanoparticle-based delivery system consisting of a hydrophobic polycaprolactone core and a hydrophilic Pluronic® F68 shell, loaded with triamcinolone acetonide and evaluated its efficacy in a DR rat model. After being administered as eye drops, the drug loaded nanoparticles significantly improved structural (retinal thickness and vascular health) and functional activity (rod and cone function) of retina as compared to DR controls that were treated with the drug alone or placebo nanoparticles. Furthermore, drug loaded nanoparticles reduced retinal inflammation as evidenced by a decrease in NF-κB, ICAM-1 and TNFα expression after 20 days of treatment. Similarly, a reduction in glial cell hyperplasia as evidenced by reduced GFAP expression, and a decrease in microvascular complications as evidenced by a decrease in VEGF secretion and microvascular tuft formation were observed in rat retinas after 40 days of treatment. The combined reduction in retinal inflammation and vascular abnormalities, both hallmarks of DR, demonstrates the potential of the nanoparticulate delivery system for use as a topical formulation for treating DR.

Animal Models of Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is one of the most common complications associated with chronic hyperglycemia seen in patients with diabetes mellitus. While many facets of DR are still not fully understood, animal studies have contributed significantly to understanding the etiology and progression of human DR. This review provides a comprehensive discussion of the induced and genetic DR models in different species and the advantages and disadvantages of each model.

RECENT FINDINGS

Rodents are the most commonly used models, though dogs develop the most similar morphological retinal lesions as those seen in humans, and pigs and zebrafish have similar vasculature and retinal structures to humans. Nonhuman primates can also develop diabetes mellitus spontaneously or have focal lesions induced to simulate retinal neovascular disease observed in individuals with DR. DR results in vascular changes and dysfunction of the neural, glial, and pancreatic β cells. Currently, no model completely recapitulates the full pathophysiology of neuronal and vascular changes that occur at each stage of diabetic retinopathy; however, each model recapitulates many of the disease phenotypes.

Early Minocycline and Late FK506 Treatment Improves Survival and Alleviates Neuroinflammation, Neurodegeneration, and Behavioral Deficits in Prion-Infected Hamsters

Prion infections of the central nervous system (CNS) are characterized by initial reactive gliosis followed by overt neuronal death. Gliosis is likely to be caused initially by the deposition of misfolded, proteinase K-resistant, isoforms (termed PrPSc) of the normal cellular prion protein (PrPc) in the brain. Proinflammatory cytokines and chemokines released by PrPSc-activated glia and stressed neurons may also contribute directly or indirectly to the disease development by enhancing gliosis and inducing neurotoxicity. Recent studies have illustrated that early neuroinflammation activates nuclear factor of activated T cells (NFAT) in the calcineurin signaling cascade, resulting in nuclear translocation of nuclear factor kappa B (NF-κB) to promote apoptosis. Hence, useful therapeutic approaches to slow down the course of prion disease development should control early inflammatory responses to suppress NFAT signaling. Here we used a hamster model of prion diseases to test, for the first time, the neuroprotective and NFAT-suppressive effect of a second-generation semisynthetic tetracycline derivative, minocycline, versus a calcineurin inhibitor, FK506, with known NFAT suppressive activity. Our results indicate that prolonged treatment with minocycline, starting from the presymptomatic stage of prion disease was more effective than FK506 given either during the presymptomatic or symptomatic stage of prion disease. Specifically, minocycline treatment reduced the expression of the astrocyte activation marker glial fibrillary acidic protein and of the microglial activation marker ionized calcium-binding adapter molecule-1, subsequently reducing the level of proinflammatory cytokines interleukin 1β and tumor necrosis factor-α. We further found that minocycline and FK506 treatment inhibited mitogen-activated protein kinase p38 phosphorylation and NF-κB nuclear translocation in a caspase-dependent manner, and enhanced phosphorylated cyclic adenosine monophosphate response element-binding protein and phosphorylated Bcl2-associated death promoter levels to reduce cognitive impairment and apoptosis. Taken together, our results indicate that minocycline is a better choice for prolonged use in prion diseases and encourage its further clinical development as a possible treatment for this disease.

miR-146a Attenuates Inflammatory Pathways Mediated by TLR4/NF-κB and TNFα to Protect Primary Human Retinal Microvascular Endothelial Cells Grown in High Glucose

Pathological mechanisms underlying diabetic retinopathy are still not completely understood. Increased understanding of potential cellular pathways responsive to hyperglycemia is essential to develop novel therapeutic strategies for diabetic retinopathy. A growing body of evidence shows that microRNA (miRNA) play important roles in pathological mechanisms involved in diabetic retinopathy, as well as possessing potential as novel therapeutic targets. The hypothesis of this study was that miR-146a plays a key role in attenuating hyperglycemia-induced inflammatory pathways through reduced TLR4/NF-κB and TNFα signaling in primary human retinal microvascular endothelial cells (REC). We cultured human REC in normal (5 mM) glucose or transferred to high glucose medium (25 mM) for 3 days. Transfection was performed on REC with miRNA mimic (hsa-miR-146a-5p). Our results demonstrate that miR-146a expression was decreased in human REC cultured in high glucose. Overexpression of miR-146a using mimics reduced the levels of TLR4/NF-κB and TNFα in REC cultured in high glucose. Both MyD88-dependent and -independent signaling were decreased by miR-146a overexpression in REC in high glucose conditions. The results suggest that miR-146a is a potential therapeutic target for reducing inflammation in REC through inhibition of TLR4/NF-κB and TNFα. Our study will contribute to understanding of diabetic retinal pathology, as well as providing important clues to develop therapeutics for clinical applications.

Evaluation of Effect of Topical Tacrolimus Treatment on Herpetic Stromal Keratitis in a Rat Model

OBJECTIVES

To investigate the effectiveness of topical tacrolimus treatment on herpetic stromal keratitis (HSK) in a rat model.

METHODS

The development of HSK was monitored for 14 days after the inoculation of rats with herpes simplex type 1 virus. Rats that developed HSK were divided into four groups as follows: (1) topical antiviral treatment (control), (2) topical antiviral and 1% prednisolone acetate, (3) topical antiviral and 0.03% tacrolimus ointment, and (4) topical antiviral plus 0.1% tacrolimus ointment. After 14 days of treatment, the severity levels of HSK were scored and compared with the levels before the treatment. The expression of CD3, CD4, and CD8 was evaluated by flow cytometry. The development of the disease was evaluated clinically and histologically.

RESULTS

Significant improvement in vascularization was observed in the groups with the drug treatment in addition to the antiviral agent (P<0.05), but there was no obvious difference within groups 2, 3, and 4 in the vascularization severity. The regression of corneal edema was 8.05%±6% in group 1, 25.17%±14.55% in group 2 (P=0.01), 36.40%±21.69% in group 3 (P=0.03), and 46.39%±14.96% in group 4 (P=0.00). A significant decrease in the number of inflammatory cells in the groups with the drug treatment was evaluated by immunohistochemical staining and confirmed by flow cytometry analysis.

CONCLUSIONS

Topical tacrolimus treatment caused a significant decrease in corneal vascularization accompanied by a lower number of inflammatory cells in the experimental HSK corneal edema model. Therefore, topical tacrolimus has the potential to be used in the treatment of HSK.

Choosing preclinical study models of diabetic retinopathy: key problems for consideration

Diabetic retinopathy (DR) is the most common complication of diabetes mellitus in the eye. Although the clinical treatment for DR has already developed to a relative high level, there are still many urgent problems that need to be investigated in clinical and basic science. Currently, many in vivo animal models and in vitro culture systems have been applied to solve these problems. Many approaches have also been used to establish different DR models. However, till now, there has not been a single study model that can clearly and exactly mimic the developmental process of the human DR. Choosing the suitable model is important, not only for achieving our research goals smoothly, but also, to better match with different experimental proposals in the study. In this review, key problems for consideration in choosing study models of DR are discussed. These problems relate to clinical relevance, different approaches for establishing models, and choice of different species of animals as well as of the specific in vitro culture systems. Attending to these considerations will deepen the understanding on current study models and optimize the experimental design for the final goal of preventing DR.

Animal models of diabetic retinopathy: summary and comparison

Diabetic retinopathy (DR) is a microvascular complication associated with chronic exposure to hyperglycemia and is a major cause of blindness worldwide. Although clinical assessment and retinal autopsy of diabetic patients provide information on the features and progression of DR, its underlying pathophysiological mechanism cannot be deduced. In order to have a better understanding of the development of DR at the molecular and cellular levels, a variety of animal models have been developed. They include pharmacological induction of hyperglycemia and spontaneous diabetic rodents as well as models of angiogenesis without diabetes (to compensate for the absence of proliferative DR symptoms). In this review, we summarize the existing protocols to induce diabetes using STZ. We also describe and compare the pathological presentations, in both morphological and functional aspects, of the currently available DR animal models. The advantages and disadvantages of using different animals, ranging from zebrafish, rodents to other higher-order mammals, are also discussed. Until now, there is no single model that displays all the clinical features of DR as seen in human. Yet, with the understanding of the pathological findings in these animal models, researchers can select the most suitable models for mechanistic studies or drug screening.